can't find file to patch at input line 3
Perhaps you should have used the -p or --strip option?
The text leading up to this was:
--------------------------
|--- /etc/httpd/conf/httpd.conf_original 2012-04-26 13:36:08.331068438 +0200
|+++ /etc/httpd/conf/httpd.conf 2012-04-26 14:27:36.857075085 +0200
--------------------------
File to patch:

By default, patch ignores the directory portion of the target filename; it's just looking for "httpd.conf" in your current working directory. If you want it to use the full path, you have to explicitly ask it to do so with the -p option:

patch -p0 < httpd.patch

(The number after -p tells it how many levels to remove from the filename path; -p N strips off everything up to and including slash number N.)

In general, you might be better off not relying on having the full path in the patch file, though; the patch will be more generally useful if it works even for files in a different directory layout. You can always cd into the directory containing the file before running patch (and use a full path to find the patch file itself, if needed, instead).